Submerged bridge or tunnel construction



Aug. 13, 1940. A. J. wlDMER SUBMERGED BRIDGE 0R TUNNEL CONSTRUCTIONFiled Aug. '7, 1.955v

3 Sheets-Sheet l.

Illlmmhnmllll Aug. 13, 1940. A.J.w1DMER SUBMERGED BRIDGE 0R TUNNELCONSTRUCTION l Filed Aug; 7, 1935 3 Sheets-Sheet 2 Aug. 13, 1940. N A.J. wlDMER SUBMERGED BRIDGE 0R TUNNEL CONSTRUCTION Filed Aug. '7, 1935 3Sheets-Sheet 3 @Jai Z5 ox? Patented Aug. 13, 1940 PATENTv OFFICESUBMERGED BRIDGE OR TUNNEL CONSTRUCTION Arthur J. Widmer, WebsterGroves, Mo.

Application August 7,

4 Claims.

My invention relates to tunnels. With many streams, such as theMississippi River, the distance from the water to bedrock is so greatand the material of the bed so unstable and so liable to scour that ithas heretofore been impracticable to build a tunnel through such bed.'I'he principal object of the present invention is to devise aconstruction which, with attributes of both a tunnel and a bridge, issuitable for use in the unstable bed below the water and will continueto function even though the 4surrounding solid matter is washed away.Another object is to devise a tunnel construction which will be stable,rigid and capable of sustaining substantial vertical and horizontalstresses or loads in addition to the hydrostatic pressures to which itis exposed. Another object is to locate the bottom of the tunnel at lessdepth below the surface of the stream than has heretofore been prac'-ticable consistently with the requirements of navigation. Another objectis. to make it practicable to build a tunnel in long sections in a safeand convenient place and float such sections to piers previously builtto receive them. Another 25 object is to utilize the current as a meansof increasing or modifying the net vertical'load on the tunnel. Anotherobject is to devise a tunnel whose drainage will not be impaired bydeflection of the tunnel under load. Another object is. to devise atunnel of such cross section as to cause minimum obstruction to the flowof the stream, especially in flood stage. Another object is to minimizethe effect of the downstream pressure of the current. Another object isto provide a 3,5 more direct and easier passage across the main chamberof incoming fresh air and outgoing foul air. Other objects are to devisean economical construction and to achieve advantages. hereinafterappearing.

The invention consists partly in locating the tunnel proper in or belowthe water and far enough down to meet the requirements of navigation andin mounting the tunnel proper, after the manner of bridges, on piersthat rest on bed- 45 rock or that rest beneath the lowest plane at whichscouring is possible, on piles or other substantial supporting medium.The invention also consists in so making the tunnel of reinforcedconcrete that it is adapted not only to withstand the hydrostaticpressure thereon but is adapted to act as a hollow box cantilever orother type of girder in resisting both vertical and horizontal stressesthereon. The invention also consists in making the tunnel with arelatively wide and low main chamber of generally oblong shape and 1935,serial No. 35,032

(ci. s1-42) with upstream and downstream extensions forming chambersthat serve for fresh air and foul air flues and other purposes. It alsoconsists in making such upstream and downstream extensions in thegeneral form of triangles which have their apexes outermost andpreferably with the outer surfaces of the inclined sides shaped toconform more or less closely to the requirements of stream-lining or soarranged that the pressure of the current will produce a verticallyacting re- 10 sultant force that lightens or increases the net verticalload on the tunnel. The invention also consists in the process ofbuilding the sections of the tunnel proper at a convenient location,closing the ends thereof for the sake of buoyancy and then floating saidsections to their places on the piers. The invention also consists inthe method and in the parts and in the combinations and arrangements ofparts hereinafter described and claimed.

In the accompanying drawings, wherein like reference numerals refer tolike parts wherever they occur:

Fig. 1 is a transverse cross sectional view of a stream crossed Xby asubmerged bridge,

Fig. 2 is a transverse cross sectional view of a stream in which thetunnel sections are entirely surrounded by water,

Fig. 3 is an isometric projection of a pier supporting a tunnel section,

Fig. 4 is a side elevation partly in section of the connection ofadjacent tunnel sections,

Fig. 5 is a transverse cross section of a preferred design of tunnelsection,

Fig. 6 is a transverse cross section of another tunnel section,

Fig. 7 is a transverse cross section of a tunnel section embodyingstructural steel members in the vertical walls;

Fig. 8 is a side elevation of a tunnel construction mounted on a pier asa balanced cantilever,

Fig. 9 is a side elevation of a tunnel construction in which a metalbolster caps a pier,

Fig. 10 is a diagrammatic transverse cross section of a tunnel sectionin which the top of the section extends horizontally throughout the fullwidth of the section,

Fig. 11 is a diagrammatic transverse cross sec.- tion of a tunnelsection in which the bottom of the tunnel section extends horizontallythe full width of the section,

Fig. 12 is a diagrammatic transverse cross section of a tunnel sectionin which the exterior surfaces of the top side portions are at a smallerangle with the horizontal than the exterior surfaces of the bottom sideportions,

Fig. 13 is a diagrammatic transverse cross section of a tunnel sectionin which the exterior surfaces of the bottom side portions have agreater area than the exterior surfaces of the top side portions,

Figs. 14 and 15 are transverse cross sections of tunnel sections havingtriangular chambers on the downstream side,

Fig. 16 is a diagrammatic transverse cross seotion of a tunnel sectionembodying the main tensile reinforcement and some of the diagonaltension reinforcement of a tunnel section designed as a cantilever toresist a downward vertical load,

Fig. 17 is a diagrammatic transverse cross section of a tunnel sectionembodying the main tensile reinforcement and stirrups of a tunnelsection acting as a cantilever' against the horizontal stream thrustmoving in the direction indicated by the arrow, and

Fig. 18 is a diagrammatic transverse cross section of a tunnel sectionembodying the principal reinforcing steel required to resist hydrostaticpressure.

The ordinary tunnel is supported more or less continuously throughoutits length by more or less stable ground and is subject to pressure ofthe surrounding water, soil or solid matter, whereas the typical bridgeis supported on widely spaced piers and is designed principally to carryits own weight and superimposed load. The structure of the presentinvention embodies characteristics of both tunnels and bridges as it iscomposed of sections that will withstand considerable hydrostaticpressure and are supported wholly or partly on widely spaced piers andare designed to take care of vertical and horizontal loads or stressesof non-hydrostatic origin.

In consequence of the design of my construction it becomes practicableto locate the tunnel proper at any desired depth below the surface ofthe water provided it does not interfere with navigation. In the case ofdeep streams, the water may completely surround the tunnel; in the caseof shallow streams, the tunnel may be wholly below the stream; and inother cases, the tunnel may be partly in the water and partly in the bedof the stream.

According to the present invention, series of piers i are built up frombelow the stream and extend high enough for the tunnel proper to restupon. These piers may rest on bedrock or upon piles or other suitablesupports Provided therefor beneath the lowest plane at which scouring ofthe river bed is anticipated.

These piers l are relatively narrow crosswise of the stream but on thedownstream side they may slope to bedrock or other support at aconsiderable angle and thus afford increased stability against tliethrust of the current on the tunnel and piers or they may be guyedupstream near their tops or may be vertically anchored at their bottomnear the upstream edges or otherwise stabilized. The tops of the piers,at their downstream ends, preferably project vertically above the maintop surface of the pier so as to constitute abutments 2 for thedownstream side of the tunnel sections 3 to bearagainst. The uppersurfaces of these abutments or vertically extending portions of thepiers preferably ccnform to the under surfaces of the downstreamportions of the tunnel sections so as to support said portionshorizontally as well as vertically.

The tunnel proper comprises one or more alined sections of reinforcedconcrete that arc preferably pre-cast at a convenient location and movedas individual units to the piers. Many factors enter into the design ofthe tunnel sections. In the first place, they must be designed towithstand the hydrostatic or soil pressure in accordance with well knownprinciples. Hydrostatic pressure, as used herein, refers to the pressureof the weight of the water on the tunnel sections and does not refer tothe pressrlre of the stream current. In the second place, the tunnelsections are designed to act as hollow box beams, preferably of thecantilever type in carrying their own weight and vertically appliedload. They are also designed to act as hollow box beams or cantileversin resisting the horizontal pressure of the moving stream. In additionto the foregoing factors, the tunnel units are designed to minimize theeffect of stream pressure after the manner of streamlining and byminimizing the vertical height thereof and to make use of the streampressure by creating vertically acting components to increase ordecrease the net vertical load on the structure. Another importantfactor is the need for .effective ventilation. All of these factors areprovided for in the construction herein described.

The main chamber fl of the tunnel section 3 has vertical side walls ofreinforced concrete and top slabl 5 and bottom slab 'I of reinforcedconcrete which are monolithic with the side walls. In the preferreddesign illustrated in Fig. 5, the top and bottom slabs are extendedhorizontally beyond the side walls and, beyond such horizontalextensions, one or both of said slabs are inclined to meet each other atthe outermost sides of the structure, thereby forming pointed tips orlow side walls 8 that are heavily reinforced and monolithic with therest of the section. Preferably the construction of the downstream sideof the tunnel section is substantially the same as the construction ofthe upstream side. In the preferred form, the crosssectional outline ofthe tunnel section is substantially a hexagon with relatively widehorizontal top and bottom and with two inclined faces 9, i@ at eachside. The main vertical walls divide the sections into a main chamber lof the general form of an oblong or rectangle of greater width thanheight and two side chambers l l of general triangular form.

In consequence of this arrangement, under hydrostatic pressure, the topand bottom slabs act in a transverse direction as beams continuous overthe side walls of the main chamber. In consequence of their continuousbeam action resulting from this arrangement it is feasible to graduallyreduce the thickness of the top and bottom slabs away from the verticalwalls after the manner of beams of uniform strength. This gradualthinning of the slabs saves considerable weight and material Withoutsignificant deviation from their horizontal disposition. It also permitsthe upper surface of the bottom of the main chamber to slope downwardlyto the middle thereof and form an efficient drain l2.

For the purpose of carrying its own weight and vertical superimposedloads, each tunnel section is designed as a longitudinally extendinghollow box cantilever or other type of beam and is reinforcedaccordingly; that is, when it is infeo Aproposed pier sites.

.the current. against deflection due to horizontal thrust than tendedthat the middle of the tunnel section shall -rest on a pier, suchsection constitutes a cantilever in which the top slab acts inlongitudinal tension and thebottom slab actsin longitudinal compressionand are reinforced accordingly, while the vertical walls act as the webmembers of such hollow cantilever and areV reinforced to take care ofthe shearing and diagonal stresses accordingly. It is noted that thetriangular side portions of the tunnel sections act in the same manneras the main oblong portion in taking care of vertical load so that thefull width of the .tunnel section functions as a cantilever.

The vertical load on a tunnel section acting as a cantilever or othertype of beam may be regulated considerably by varying the buoyancy ofthe tunnel section and also, where advisable, by utilizing, in themanner elsewhere described, the

-vertical component of the force of the current on the inclined sides.Therefore frequently in designing and in determining the proper span ofa tunnel section, the amount of the more difiicultly regulablehorizontal thrust of the current will be a governing factor.

In bridging a stream with a submerged Way resting on piers many peculiarconditions and difficulties may be encountered under water at Greatereconomy and better design of the whole structure results if elasticityis available with respect to number, location and spacing of piers andalso with respect to the character of beam supported by the piers.

The shape and proportions of the tunnel section which I prefer offersgreat strength as a beam resisting vertical load and relatively evengreater strength as a horizontal beam resisting The section is also morerigid against deection due to Vertical load. Because of the relativelygreat expense of piers, it is apparent that economy of construction liesin selecting as long spans as possible and that spans less than about21/2 -times the width of the tunnel sections will not generally proveeconomical. Furthermore since cantilever beams offer relatively morerigidity against deflection than freely lsupported beams, it willfrequently be advantageous in increasing the spans and reducing thenumber of piers required, to so rest the tunnel sections about midway oftheir length on the piers that the sectionsact as balanced cantileverbeams, extending longitudinally in both directions beyond the piers. Toprovide such cantilevers through the use of my tunnel sections requiresonly suitable quantity and arrangement of tensile steel reinforcement inthe sections in the usual manner to take care of the negative bendingmoments producedy by the non-hydrostatic vertical and horizontal loads,and such supplementary reinforcement and design precautions as arecommon in the art of reinforced concrete, Cantilever design oiersnumerous advantages; for example, with tunnel sections of equal length,cantilevers will in a total given distance require one less supportingpier than simple beams. Cantileversl necessairly require broad pierseats to prevent tipping from unequal loading of the balanced ends butthe increased pier breadth is re1- atively inexpensive and may beautomatically compensated for by increasing the length of the tunnelsection.

Floating debris or ice may produce varying horizontal loads on opposedends of cantilevered sections as described, and the vertical loads oftraflic may not be uniform throughout the length of a tunnel section.Full consideration of these unbalanced loads of oppositely extendedsubmerged cantilevers is extremely important because, Whereas inordinary cantilever bridge construction the live loads are generallysmall compared to the dead loads, the buoyant tendency of the tunnelsection of the submerged bridge may frequently almost completelyneutralize or even exceed the dead weight of the structure. Thus thelive loads assume relatively great importance and may govern the design.In cantilever design as described I nd it advisable to provide, betweenthe tunnel sections and the piers, anchor bolts I3 or other anchoringmeans of any suitable nature near the longitudinal extremities of thepier to resist tendency to tip under unbalanced loading of the opposedcantilevers, and in certain cases bearing shoes may be necessary at thepier seats to prevent crushing of the concrete.

Completely efcient cantilever bridge design generally indicatessubstantial increase in the depth of the cantilever tunnel sections atthe support. However, such increase would tend to cause objectionableobstruction to the stream flow and to create excessive tendency tooverturning of the pier, as stream-lining such a consequently largeobstacle would be difcult. Furthermore there might be difficultiesincident to launching and floating such tunnel sections if built at theshore. Under conditions necessitating extreme length of cantilever, itmay be desirable to use a metal bolster I4, which rests on and, ineffect, constitutes part of the Dier. Such bolster is designed as acantilever extending longitudinally beyond the pier in both directionsand formed of suitable shapes to reduce resistance to the stream, saidbolster being more or less open in construction in the direction of thestream. This bolster, if desired, may be made:

completely permanent with respect to corrosion or similar deteriorationthrough the use of selected alloys of metal. To assist in resistingoverturning due to unbalanced loads in the oppositely extended tunnelsection cantilevers, which may extend considerable distance beyond theextremities of the bolster, the metal bolster is firmly anchored nearthe longitudinally opposite sides of the pier by means of suitablyarranged bolts I5 or any other suitable and adequate means; and thetunnel section is similarly anchored to the bolster or the pier or toboth. Seats I6 are provided of suitable character on the bolster for thetunnel section. It is obvious that under certain conditions I may use abolster of reinforced concrete construction in lieu of the metal bolsterjust described.

As indicated above, the tunnel sectionsl are designed to act as hollowcantilever girders in resisting the horizontal pressure of the stream.In such action, the upstream side of a tunnel section, including theupstream vertical wall, is in the region of tension and reinforcedaccordingly; and the downstream side, including the downstream Verticalwall, is in the region of compression and reinforced accordingly wherenecessary, while the top and bottom slabs act as webs of the cantileverand are reinforced accordingly for shearing and diagonal tension. Thehorizontal pressure against the tunnel sections is transmitted to theabutment provided therefor on the piers.

In practice, it is desirable to pre-cast each tunnel section at someconvenient place, float it through the water to a point above th-e pierand then lower it into vits position on the pier and against theabutment provided thereon for it. For the purpose of moving such asection, its ends are rst closed by means of removable bulkheads andother temporary bulkheads may be used to divide the main chamber intosmaller compartments and, if the section itself is not sufficientlybuoyant to oat or floats too low in the water, pontoons or othersuitable means are used to provde additional buoyancy. Then the sectionis towed to a point above the pier and its buoyancy is decreasedgradually, as by properly slackening the cables of the pontoons or byadmitting water into the tunnel compartments, so as to lower the sectiononto the pier. If the top of the pier is lower than the bottom of thestream, the bottom is dredged out or removed by any suitable means farenough to seat the tunnel section on the pier; and after the tunnelsection is seated on the pier and suitably secured thereto, thesurrounding cavity is allowed to silt up under the action of the stream.The temporary bulkheads are removed after adjacent sections have beenconnected and made watertight by any suitable means and the water andany silt which may have entered the section are removed. In case thetops of the piers are lower than the existing loose bed of the stream,way for the tunnel sections may be provided as previously described orthe sections may be rst lowered on the loose bed after which the loosematerial is removed by any suitable means to permit lowering thesections on the piers.

In the case of cantilever sections, the ends of the sections arepreferably provided with suitable connecting devices for joining themtogether in alinement either directly or through a short connectingsection especially provided for the purpose. In either case, it isdesirable to have the ends of the cantilever sections provided withradially extending rings or arms l1 firmly anchored in the reinforcedconcrete and provided with tie bolts I8 adapted to pass through similarrings or arms provided to receive them on the adjacent section.

In designing the tunnel sections to resist hydrostatic pressure, the topslab 6 and bottom slab 'i of the main chamber are treated as beamssupported by the vertical walls 5. In my invention, I prefer to have onemain chamber 4 and two side chambers l I as shown in Fig. 5, becausecontinuous beam action is thereby assured, especially for the relativelylong central slabs which form the top and bottorrr of the main chamber.The top and bottom slab extensions 9, i forming the side chambers, attheir outer extremities merge and support each other and at their innerextremities rest on the vertical walls 5. It is desirable that the slabs9, ID have horizontal portions i9 substantially in the plane of the topand bottom slabs 6, 'I because they improve the condition of continuityover and adjacent to the vertical supports. By providing this continuousbeam action with its consequently reduced bending moments, I am able toeffect economy in structural materials. Also I may use thinner slabs toreduce weight or I may accomplish this purpose by designing the slabwithin practical limits as a beam of uniform strength thus obtaining aslab of varying thickness and thus improve the buoyant condition of theentire section.

The use of a central main chamber and two side chambers to `create threecontinuous spans provides another great advantage with respect to thereduction of weight of the tunnel section. Hool, in vol. 3, page 443, ofhis book entitled Reinforced Concrete Construction (1st edition, 1916),shows how four walls similar to the top, bottom and sides of the mainchamber 4, when the top and bottom are under hydrostatic pressure, maybe treated in the manner of a symmetrical arch vwith fixed ends, withthe resulting moments in the top and bottom slabs very similar, if notidentical, to lthose of the continuous beams previously mentioned.However, in order to create this condition the vertical walls 5,particularly at their extremities, must substantially equal in thicknessthe top and bottom slabs at their supports. Therefore, if designedaccording to the above arch theory, as increases in hydrostaticpressures increase the thickness of the top and bottom slabs, so alsomust the vertical walls increase in thickness and weight. Under themethod of design set out in the preceding paragraph (since in designingfor hydrostatic pressure the walls are considered merely as supports,and for this purpose require only relatively small areas of concrete),increases in weight of the top and bottom slabs may be compensated forby reducing the Ithickness and weight of the vertical walls. Since theseWalls serve also as beam webs in the treatment of the entire section asa beam under vertical load, this reduction in the thickness of thevertical walls may be accompanied by the use of either a thin steelgirder 2U to take non-hydrostatic vertical loads as indicated in Fig. 7,or by the use of a thin reinforced concrete wall with suitablestructural steel sections introduced, in designing for thenon-hydrostatic vertical loads, as a supplementary means ofstrengthening or assisting said reinforced concrete wall.

In the central slab of three uniformly loaded continuous spans thepositive bending moment at the center of the span is only one-half asgreat as the negative bending moment at the supports. Advantage is takenof the reduced moment to reduce the slab thickness in the center of thebottom slab of the main chamber to create a central longitudinal gutteror drain as indicated at l2. The finished roadway surface of a vehiculartunnel may be a thin cement or mastic coating of uniform thicknessapplied directly on the reinforced concrete bottom slab to maintain thedrain in the center, or the slab itself may form the roadway surface.

In the interior` span of a uniformly loaded beam continuous throughthree spans, the maximum bending moment is the negative moment over thesupports. This is twice the amount of the positive bending moment in thecenter of the span. The point of contra-exure is about twenty-oneone-hundredths of the span from the support; therefore the bendingmoment decreases very rapidly from the support. For example, in a spanof twenty-one feet, under about five thousand pounds per square foothydrostatic pressure, the moment has decreased suiciently one foot fromthe support to permit nearly twelve inches reduction in the thickness ofthe slab from about thirty-nine inches thickness required at thesupport, while six inches still further away about sixteen inches totalreduction in thickness is possible without increase in the tensile andcompressive stresses in the steel and concrete. A theoretically idealcondition would be realized if the floor slab forming the bottom of themain chamber were altered in thickness through its entire length tocorrespond exactly with the changes in the bending moment. However,shearing stresses and other considerations make it impractical torealize the ideal condition. Normally in a structure as described,except adjacent to the supports, it will be desirable merely toapproximate the minimum slab thicknesses permitted by consideration ofthe tensile and compressive stresses only. However, near the supportsadvantage may be taken of the rapidly decreasing bending moment sharplyto reduce the slab thickness. Such designmay be used to provide sharpupward inclines in the top surface of the chamber bottom at its sides asindicated at 2|. These sharp inclines form brackets at the sides of theroadway and thus create effective wheel guards for vehicles. Obviously,if desirable to provide increased effectiveness as wheel guards, theinclined surfaces may be altered in angle and position but should notlie within the surfaces established by the structural design.

The construction hereinbefore described is especially useful in the caseof streams whose beds are liable to scour for a considerable depth intime of ood. In such case, the tunnel is located at a level that isdetermined by considerations of economy and the requirements ofnavigation rather than by the soil and water conditions and may normallybe embedded in the silty or gravelly matter that forms the bed of thestream and remains more or less stationary under normal conditions butis likely to scour to a considerable depth in time of flood and therebyleave the tunnel sections supported wholly by piers after the manner ofbridges. My construction is well adapted to meet these conditions andthe stream-lining thereof minimizes its effect as an obstruction to thecurrent.

Another important advantage of the construction hereinbefore describedis that its at top and bottom are well adapted for resisting stressesdue to cantilever or other type of beam action and permit the verticalheight of the tunnel sections to be reduced fairly close to the heightneeded for the accommodation of traic. This reduction in the heightreduces the area of resistance to the pressure of the stream and alsoenables the bottom of the tunnel sections to be located at a higherlevel and consequently where the hydrostatic pressure is less than wouldother- Wise be practicable.

Another important advantage is the streamlining effect arising from thesloping of the upstream and downstream sides of the tunnel. The idealcondition for stream-lining would call for the surfaces of the sides tobe reverse'ly curved with the concave surface portions outermost on both.upstream and downstream sides; but for practical purposes it issufficient to make such sloping surfaces substantially flat providedtheir angle with the horizontal is not more than about forty-livedegrees. For a xed position in a stream, the total horizontal thrust dueto the action of the current on a body depends upon the velocity of thecurrent, the size and shape of the body and the roughness of itssurface. If the body is pointed at both ends with its axis parallel tothe current, as in my preferred design, the stream lines on closingtogether smoothly at the downstream extremity, exert normal pressuresagainst the downstream surfaces whose components longitudinal to thesaid axis approximately balance the corresponding components of thenormal pressure on'the upstream surfaces; so that the total horizontalthrust consists mainly of that due to skin friction alone distributedalong the external surface of the body.

Since the skin friction is comparatively slight f due to the smoothnessof the external surfaces of my tunnel sections, I prefer to approximatethe ideal condition by shaping the downstream extremity similar to theupstream extremity.

Another important advantage is that the sloping sides of the tunnelproper may be optionally so designed that the pressure of the currentwill act either in aid of or against the buoyancy of the construction,as the pressure of the current is normal to the surface of the tunnelsections and varies as the sine of the angle between the direction ofthe current and such surface. Thus, if as in Fig. 10, the top of thetunnel section extended horizontally throughout the full width of thesection, while the side portions of the section sloped all the way frombottom to top, the pressure of the stream would have an unbalancedcomponent acting vertically upwardly against the sloping portions and itwould thereby lessen the net vertical load required to be carried bysaid section. If it were desired to decrease the buoyance of theconstruction, the bottom of the section could be made horizontal for thefull width thereof and the side portions of the top sloped, as in Fig.1l, so that the Vertical component of the current pressure would actdownwardly thereon. As the total pressure of the current variesaccording to the area under such pressure, in some cases, it may bedesirable to slope one or both of the top side portions for a differentwidth than the bottom side portions as in Fig. 13. Regulation of the netvertical load may also be obtained by having the topand bottom of theside portions at different angles with the horizontal as in Fig. l2. Tosufciently lessen the net vertical load on the section, it may bedesirable to take advantage of the hereinbefore mentioned reduction inthe slab thickness at the center of the bottom slab of the main chamberto create further inclined surfaces against which the current may act inthe manner just described. Such inclined surfaces may be provided bykeeping the upper surface of the bottom slab horizontal and incliningthe bottom surface upwardly from the sides thereof as shown at 22 inFig. 6.

Another important advantage of my construction is that it provides avery eflicient system of ventilation. For this purpose one of the sidetriangular chambers may serve as the fresh air duct and the other sidetriangular chamber may serve as the foul air duct, suitable openings 23being formed through the vertical walls at intervals throughout thelength of the wall and at various heights. By this arrangement, the airpasses more or less horizontally from one side duct to the other, beingpreferably propelled or drawn by suitable blowers or fans provided forthe purpose.

In the foregoing description, I have described each tunnel section asseated at its middle on a single pier. With a long section and a narrowpier, a heavy unbalanced live load would tend to unbalance such astructure. For this reason, I prefer to cap the pier with a ,wide metalbolster firmly secured thereto by -bolts or otherwise and havingprojecting brackets 24 firmly braced against and secured to the sides orthe top adjacent to the sides of the pier. The tunnel section is seatedon said bolster and firmly secured by bolts or otherwise to the widespreading brackets of said bolster. The wide bearing and anchorage thusafforded for the tunnel section reduces the beam stresses therein andprotects it against imbalance under live load.

While I have hereinbefore specifically described the tunnel sections ascantilevers, it is obvious that they may be designed as simple or freelysupported beams with their ends resting on different piers or ascontinuous beams supported on several piers. In such cases, there wouldbe little, if any, difference in the shape of the structure; but thetype of beam selected would materially affect the position of the maintensile reinforcement. For example: if a cantilever is selected, themain tensile reinforcement is placed to extend longitudinally in the topmember of the tunnel section, as at 25, to resist downwardly actingnon-hydrostatic load and near the upstream side extremity, as at 25, toresist the horizontal stream thrust; while in the case of a tunnelsection freely supported at its ends, the main tensile reinforcement isplaced opposite to that just described to extend longitudinally in thebottom member of the tunnel section to resist downwardly actingnon-hydrostatic load and near the downstream side extremity to resistthe horizontal stream thrust. In the case of tunnel sections continuousover several supports, the main tensile reinforcement in the middleportion between points of contra-flexure is placed as just described forfreely supported tunnel sections, but, at and adjacent to the supports,such reinforcement is positioned after the manner used in cantilevers.Except for the different location just mentioned of the principalreinforcement as governed by the type of beam selected, the hollow beamconstruction of freely supported tunnel sections and sections continuousover several supports would be similar to and embody the advantageshereinbefore stated. fis in other engineering' structures, every tunnelwill present problems as to the amount, location and arrangement of thereinforcement used therein, but, with the guidance afforded by tl 'sspecification, such problems are well within the skill of engineersfamiliar with the reinforcement of concrete.

In cases where it may be desirable to increase or decrease the buoyancyof the tunnel sections by making the top or bottom horizontal for thefull width of the section as previously described herein, it is obviousthat a very deep beam is formedby the wide top 2l or bottom 28 whichmight be capable in itself, if properly reinforced, of resisting all thestresses induced in the section by the horizontal stream thrust. In suchcase, this deep beam alone might be designed to carry either all of thehorizontal load or all of the shear and diagonal tension resulting fromthe horizontal load.

Hereinbefore I have described a submerged bridge composed of severaltunnel sections and piers. However, since a tunnel section may beseveral hundred feet long, it is obvious that one such section may sulceto cross a relatively narrow waterway. In such cases the tunnel sectionmay either be cantilevered from a pier near the middle of the stream, orsupport for the single tunnel section may be furnished by two piersclose to or on the stream banks.

In swift current the preferred shape of the tunnel section previouslydescribed offers many advantages, of which one is the reduction of theeffect of the horizontal thrust of the stream current on the section.However, the unit horizontal stream thrust on the tunnel section variesas the square of the current velocity so that, without adverse effect onthe net horizontal tunnel load, as slower currents are encountered, theangle of the sloping sides with the horizontal may be increased so as toapproach ninety degrees in still water. It is therefore obvious thatunder certain circumstances deviation from the preferred tunnel sectionwithout materially affecting some of its advantages may be possible. Ina relatively short tunnel in a slow current, two side Ventilatingchambers may not be needed. In such a case one triangular shapedVentilating chamber might normally be placed on the upstream side of themain tunnel chamber, but circumstances might dictate its placement onthe downstream side, and even in this position, as in Figs. 14 and 15,the resultant stream-line effect would, by elimination of downstreameddies, minimize the horizontal load on the tunnel.

When the tunnel section of preferred shape is under consideration as abeam resisting horizontal stream thrust, the neutral axis normally willlie, as at 29 or 30, in a longitudinally extending vertical plane inwardfrom the vertical wall dividing the main chamber from one of thetriangular side chambers. The side of the tunnel on which it will liedepends on the type of beam selected, and, in the case of continuousbeams, depends on the longitudinal distance, from the middle of thespan, of the transverse plane under consideration. However, if onetriangular chamber is omitted, as in Figs. 14, 15, the vertical neutralaxis just described may lie in the said vertical dividing wall, orinward from said wall as shown at 3l, if the triangular chamber extendsbut a short distance from the main chamber, or outward from said wall,as shown at 32, if the triangular chamber extends a relatively longdistance from the main chamber. In the latter case the walls or portionsof the walls forming the exterior sides of the triangular chamber mayrequire especial consideration to provide and suitably place sufficientcross-sectional area of concrete to satisfy the compressive stressesinduced in the tunnel section by the horizontal thrust.

In tunnel sections, as hereinbefore described, whichact as beams of longspan, excessive or unprovided-for deflection under load may seriouslyimpair drainage of the tunnel and provide other undesirable features. Asthe deflection under load is at least approximately calculable,

the pre-cast tunnel sections may desirably be constructed with cambersor bends opposite in direction to and about off-setting in amount theexpected deflection under load so that, when in place on the piers andunder load, each tunnel section throughout its entire length would lieas closely as practicable in the true lines vertically and horizontallyestablished as desirable for the tunnel.

Hereinbefore I have described the top and bottom of the tunnel as beingsupported against the hydrostatic pressure by means of side walls of themain chamber. In some cases it may be advisable to use spaced columns inlieu of said walls.

What I claim is:

l. An internally metal reinforced concrete construction comprising atunnel section of greater width than height and a pier constructionholding said section, said section comprising one chamber of oblongsection of greater width than height and a chamber of substantiallytriangular section monolithic with said first chamber on one of thesides thereof, said tunnel section further comprising substantiallyvertical reinforced concrete walls and substantially horizontal top andbottom members of reinforced concrete, one of said members comprisinglongitudinally extending metal reinforcement in the region of tensilestresses induced in said tunnel section by nonhydrostatic vertical load,one of said members comprising metal reinforcement in the region of andadapted to take care of the shearing stresses and diagonal tensioninduced in said tunnel section by horizontal stream thrust, saidvertical Walls comprising metal reinforcement in the region of andadapted to take care of the shearing stresses and diagonal tensioninduced in said tunnel section by non-hydrostatic vertical load, one ofsaid Walls comprising longitudinally extending metal reinforcement inthe region of and adapted to take care of the tensile stresses inducedin said tunnel section by horizontal stream thrust, and said top andbottom members comprising laterally extending metal reinforcement in theregion of tensile stresses induced by hydrostatic pressure.

2. An internally metal reinforced concrete construction comprising atunnel section of greater Width than height and a pier constructionholding said section, said section comprising one chamber of oblongsection of greater Width than height and a chamber of substantiallytriangular section monolithic with said rst chamber on one of the sidesthereof, said tunnel section further comprising substantially verticalreinforced concrete Walls and substantially horizontal top and bottommembers of reinforced concrete, one of said members comprisinglongitudinally extending metal reinforcement in the region of tensilestresses induced in said tunnel section by nonhydrostatic Vertical load,one of said members comprising metal reinforcement in the region of andadapted to take care of the shearing stresses and diagonal tensioninduced in said tunnel section by horizontal stream thrust, saidVertical walls comprising metal reinforcement in the region of andadapted to take care of the shearing stresses and diagonal tensioninduced in said tunnel section by non-hydrostatic vertical load, saidtop and bottom members comprising laterally extending metalreinforcement in the region of and adapted to take care of the tensilestresses induced by hydrostatic pressure, and the exterior Walls of saidtriangular chamber comprising longitudinally extending metalreinforcement in the region of tensile stresses induced in said tunnelsection by horizontal stream thrust.

3. An internally metal reinforced concrete construction comprising atunnel section of greater width than height and a pier constructionholding said section, said section comprising one chamber of oblongsection of greater Width than height and a chamber of substantiallytriangular section monolithic with said first chamber on one of thesides thereof, said tunnel section further comprising substantiallyVertical reinforced concrete walls and substantially horizontal top andbottom members of reinforced concrete, one of said members comprisinglongitudinally extending metal reinforcement in the region of tensilestresses induced in said tunnel section by nonhydrostatic vertical load,one of said members comprising metal reinforcement in the region of andadapted to take care of the shearing stresses and diagonal tensioninduced in said tunnel section by horizontal stream thrust, saidvertical Walls comprising metal reinforcement in the region of andadapted to take care of the shearing stresses and diagonal tensioninduced in said tunnel section by non-hydrostatic vertical load, one ofsaid Walls comprising longitudinally extending metal reinforcement inthe region of and adapted to take care of the tensile stresses inducedin said tunnel section by horizontal stream thrust, said top and bottommembers comprising laterally extending metal reinforcement in the regionof tensile stresses induced by hydrostatic pressure, and those portionsof the enclosing Walls of said triangular chamber which lie on thecompression side of the Vertical neutral axis of the said tunnel sectioncomprising sulicient crosssectional area of concrete to satisfy theprincipal compressive stresses induced in said tunnel section byhorizontal stream thrust.

4. An internally metal reinforced concrete submerged bridge constructioncomprising a tunnel section of greater Width than height and a pierconstruction holding said section, said section comprising a mainchamber of oblong section of greater width than height and substantiallytriangular chambers on the upstream and downstream sides of said tunnelsection, said tunnel section further comprising substantially verticalreinforced concrete Walls and substantially horizontal top and bottommembers of reinforced concrete, one of said members comprisinglongitudinally extending metal reinforcement in the region of tensilestresses induced in said tunnel section by non-hydrostatic verticalload, one of said members comprising metal reinforcement in the regionof and adapted to take care of the shearing stresses and diagonaltension induced in said tunnel section by horizontal stream thrust, saidtop and bottom members comprising laterally extending metalreinforcement in the region of and adapted to take care of the tensilestresses induced by hydrostatic pressure, the exterior Walls of one ofsaid triangular chambers comprising longitudinally extending metalreinforcement in the region of tensile stresses induced in said tunnelsection by horizontal stream thrust, and one of said triangular chamberscomprising in those portions of its enclosing Walls, which lie on thecompression side of the Vertical neutral axis of said tunnel sectionsufficient cross-sectional area of concrete to satisfy the principalcompressive stresses induced in said tunnel section by horizontal streamthrust.

ARTHUR J. WIDMER.

